Show captionJaylen Brown: ‘We’re having some of the same problems we had 50 years ago. Some things have changed a lot but other factors are deeply embedded in our society.’ Photograph: Brian Babineau/NBAE/Getty Images

Jaylen Brown is one the most intelligent and interesting young athletes I’ve met in years and it seems fitting that, midway through our interview in Boston, he should retell a parable that brings together Martin Luther King and the great American writer David Foster Wallace.

“We’ve got two young fish swimming one way and an older fish swimming the other way,” the 21-year-old star of the Boston Celtics says as he considers the enduring backdrop of race in the United States. “They cross paths and the older fish says: ‘What’s up guys, how’s the water?’ The two younger fish turn around and look back at the wiser fish and ask: ‘What’s water?’ They’ve never recognised that this is what they actually live in. So it takes somebody special like Martin Luther King to see past what you’ve been embedded in your whole life.”

He has also looked forward to playing in London on Thursday, against the Philadelphia 76ers, and answered a question as to whether his young Celtics team may become NBA champions in the next few seasons: “Why not this year? People say maybe we’ll be good in two years – but I think we’re good now. Right now we’ve got one of the best records in the league. I think we could be as good as we want to be. But the more we let people construct our mindset, and start saying two years from now, is the moment we lose.”

Last week the Celtics beat LeBron James’ Cleveland Cavaliers 102-88. Excitement and anticipation surrounds the Celtics but race still stalks our conversation – and it has echoed hauntingly through Brown’s life. “Racism definitely still exists in the South,” he says, remembering his youth in Marietta, Georgia. “I’ve experienced it through basketball. I’ve had people call me the n-word. I’ve had people come to basketball games dressed in monkey suits with a jersey on. I’ve had people paint their face black at my games. I’ve had people throw bananas in the stands.

“Racism definitely exists across America today. Of course it’s changed a lot – and my opportunities are far greater than they would have been 50 years ago. So some people think racism has dissipated or no longer exists. But it’s hidden in more strategic places. You have less people coming to your face and telling you certain things. But [Donald] Trump has made it a lot more acceptable for racists to speak their minds.”

Brown admits that, when he was 14, “It wounds you. But when I got older and went to the University of California [Berkeley] I learnt about a more subtle racism and how it filters across our education system through tracking, hidden curriculums, social stratification and things I had no idea of before. I was really emotional – because one of the most subtle but aggressive ways racism exists is through our education system.”

In his year at college, before pausing his degree to play in the NBA, Brown wrote a thesis about how institutionalised sport impacts on education. “I was super emotional reading about it,” he says of his chosen subject. “There’s this idea of America that some people have to win and some have to lose so certain things are in place to make this happen. Some people have to be the next legislators and political elites and some have to fill the prisons and work in McDonald’s. That’s how America works. It’s a machine which needs people up top, and people down low.

“Even though I’ve ended up in a great place, who is to say where I would’ve been without basketball? It makes me feel for my friends. And my little brothers or cousins have no idea how their social mobility is being shaped. I wish more and more that I can explain it to them. Just because I’m the outlier in my neighbourhood who managed to avoid the barriers set up to keep the privileged in privilege, and the poor still poor, why should I forget about the people who didn’t have the same chance as me?”

What did he think of Colin Kaepernick’s protest against police brutality and racism – which the former San Francisco 49ers quarterback began even before Trump’s election to the White House? “It was peaceful and successful. It made people think. It made people angry. It made people want to talk. Often everybody is comfortable with their role in life and they forget about the people who are uncomfortable. So for Colin to put his career on the line, and sacrifice himself, was amazing. But Colin was fed up with the police brutality and pure racism. He speaks for many people in this country – including me.”

Did Brown understand from the outset that Kaepernick’s career was in jeopardy? “Absolutely. I wasn’t shocked how it turned out. Colin was trying to get back into the NFL and find another team and he’s more than capable. But I knew it was over. I knew they weren’t going to let him back. Nobody wanted the media attention or to take the risk. They probably just wanted to blackball him out of the league.

“That’s the reality because sports is a mechanism of control. If people didn’t have sports they would be a lot more disappointed with their role in society. There would be a lot more anger or stress about the injustice of poverty and hunger. Sports is a way to channel our energy into something positive. Without sports who knows what half of these kids would be doing?

“We’re having some of the same problems we had 50 years ago. Some things have changed a lot but other factors are deeply embedded in our society. It takes protests like Kaepernick’s to make people uncomfortable and aware of these hidden injustices. People are now a lot more aware, engaged and united in our culture. It takes a special person like Kaepernick to force these changes – because often reporters and fans say: ‘If you’re an athlete I don’t want you to say anything. You should be happy you’re making x amount of money playing sport. You should be saluting America instead of critiquing it.’ That’s our society.”

Has his anger been amplified during Trump’s presidency? “Not really. I just think Trump’s character and some of his values makes him unfit to lead. For someone like him to be president, and in charge of our troops? It’s scary to be honest.”

Trump’s Twitter war in November with LaVar Ball tipped the scales, for Brown, beyond credulity. The President accused Ball of being “ungrateful” – following the release from China of his son, LiAngelo, and two other UCLA basketball players after they were caught shoplifting. “He demanded a thank you,” Brown says of Trump. “It’s ridiculous. What happened to people doing things out of the generosity of their heart or because it was the right thing to do? There have been multiple situations where it’s been ridiculous but that one was like: ‘OK I’m done. I’m done listening to anything you have to say.’ A 19-year-old kid makes a mistake overseas and [Trump] demands an apology from his dad? I think Trump’s unfit to lead.”

Jaylen Brown dunks during a game against the Brooklyn Nets. Photograph: Justin Lane/EPA

Brown’s readiness to talk about politics and culture might account for the surreal suggestion in 2016 that he was “too smart” for the NBA. From the outside, ‘smart’ seemed a euphemism for ‘troublesome’. What did Brown think when, as a teenager, he heard words unlikely to be used in conjunction with a white athlete? “It was hinting at something very problematic within society. It bothered me but I was so focused on getting to where I was going I never dissected it or pointed it out to anybody.

“But I disagree that an athlete can’t be intelligent. Some people think that, in basketball, we have a bunch of masculine adults who don’t know how to control themselves. They’re feeble-minded and can’t engage or articulate ideas. That’s a narrative they keep trying to paint. We’re trying to change it because that statement definitely has a racist undertone.”

Brown chose Berkeley because he knew he would be stretched academically. Has he missed the intellectual stimulus since swapping college for professional basketball? “Absolutely. I’ve missed it so much. I’m in a good environment here but at Cal I was learning something new every day. I’m now trying to keep well-balanced instead of single-minded. I take piano lessons after I spent the last year teaching myself piano. If I’m frustrated or had a bad day, but need to keep engaged, practicing the piano does that for me. Same with the YouTube [vlogs which he makes]. I use the camera so I can show something of this life to the everyday person who is interested in seeing what it’s like for an athlete on a day-to-day basis. Everybody puts you on a pedestal especially when you’re playing well and they make it seem like you’re not human. But I’m just a regular guy.”

During his first year at Berkeley, in his spare time, Brown learned Spanish from scratch and became fluent. “I’m not as good now,” he says. “I started again because there’re so many conjugations that slip your mind if you don’t practice. But I also just learned the Arabic alphabet. I’m proud of myself because the pronunciation is hard.”

Brown starts to say the Arabic alphabet out loud and, to an untutored ear, he sounds impressive. “Yeah,” he says with a grin, “I’m trying.”

He describes himself as an introvert – and it must be hard being quiet and reflective in a boisterous sporting environment? “Absolutely. It’s not just the locker room. In life if you stay quiet you’ll get left behind. So I had to learn to be more vocal and outgoing. I just try to be respectful of everybody. But the closer you get with guys the more you talk to them. It becomes like a family – especially when you’re winning. Last year I was much quieter but this year my opinion is valued more. We have a good locker room.”

Jaylen Brown’s Celtics are set for a deep playoff run this season. Photograph: CJ Gunther/EPA

The value of that locker room was felt by Brown after the tragic suicide of his friend Trevin Steede. Brown found the will to play against the NBA champions, the Golden State Warriors, the night after Steede’s death – and he inspired the Celtics to a memorable victory by scoring the most points [22] while producing tenacious defence. After the game Kyrie Irving, the Celtics’s superstar, gave Brown the ball and said: ‘This one’s for Trevin.’

Before they played again, in Atlanta, where Steede’s family live, Brown visited his friend’s mother and other grieving relatives. He then went out and shot a career-high 27 points. “I’m so thankful for the people around me. They lifted me up. I don’t know what my mental state would be right now without them.

“I met Trevin when I moved to Wheeler – which is a big basketball school in Marietta, Georgia. Trevin was a year older so he was a sophomore and I was a freshman. They brought me in and there was only one spot left on the team and it was between me and him. They gave it to me.

“I didn’t know anybody when I first got there so at lunch in the first week I’d eat by myself – acting like I’m on my phone. Trevin came up to me after the third day. I’d seen him in workouts but I didn’t really know him. He said, ‘Man, come sit over here with us.’ Ever since then, we were best friends.”

How did he hear about Trevin’s death? “His mom called me. I’m thinking she’s just checking on me or saying hi. But she called to tell me he’s passed.”

Brown looks down and his hurt is obvious. He also admits he needed the support of Steede’s mother to face Golden State. “I probably wouldn’t have played unless she called me. Brad Stevens [the Celtics coach] asked how I was doing. I told him, ‘I don’t think I’m able to come in today. He said: ‘That’s fine. Take your time.’ Three seconds after I hung up, Trevin’s mom called. I told her I wasn’t doing well and I probably wasn’t going to play that night. She said: ‘You know that’s not what I want and that’s not what Trevin would have wanted. So if you can find it in your heart to go out and play for him, do it.’”

Did he play in a daze, or was he inspired by Trevin to help Celtics win? “I didn’t feel anything. It was like I was out there by myself.”

The chance to play in London lifts his mood. “I visited London for the first time last summer. It was great. I went to see Big Ben because one of my idols is Benjamin Banneker [the African American scientist who, among other achievements, worked with striking clocks in the 18th century].”

This week Brown would like to hear more grime and to see Arsenal. “I like Barcelona because of the players they’ve had traditionally – from Ronaldinho to Messi. I really like Arsenal too. I like their tradition, and their diehard fans. I hope to see them in London. I think Thierry Henry is going to be there so I’ll just hit him up and see if I can get some access to the [stadium] tour, get some shots on the field. Last summer I became really close with Thierry. I got to talk to him and we keep up with each other and he gives me advice – about sports and life. He’s one of the all-time greats.”

At the Celtics’ training facility, on the outskirts of Boston, Brown rises to his full 6ft 7in. He looks around the empty court before turning back with a smile when I say we’ve covered a lot of ground – from the mysteries of water for two young fish and the enduring problems of race in America to the impact of learning and the pleasure of following sport around the world. “Yeah,” Brown says softly, stretching out his hand, “that’s the way I like it”.

• The NBA London Game 2018 sees the Philadelphia 76ers host Boston Celtics at The O2 on 11 January. The game will also be live on BT Sport and NBA League Pass.